Liquid dispensing devices have been on the market for ages. Many of them rely on a pressurized gas raising the pressure in the interior of a container containing the liquid to be dispensed, in particular a beverage like beer or other carbonated beverages. The container is either prepressurized in plant or the gas is fed upon use either directly into the container containing the liquid like e.g., in U.S. Pat. No. 5,199,609 or between an external, rather stiff container and an inner, flexible vessel (e.g., a bag or a flexible bottle) containing the liquid to be dispensed, like in U.S. Pat. No. 5,240,144 (cf. FIGS. 1(a)&(b)). Both applications have their pros and cons which are well known to the persons skilled in the art. The present invention applies equally to both types of delivery systems.
The over pressure applied to the container for driving the liquid out thereof is usually of the order of 0.5 to 1.5 bar (above atmospheric). It is clear that the flow of a liquid reaching the dispensing tap at such high pressure could easily become uncontrollable and such sudden pressure drop could lead to the formation of unwanted foam. For this reason, it is often necessary to provide means for controlling the flow of a liquid out of the container and/or for smoothly reducing the pressure thereof between the container it is extracted from and the tap, where it contacts atmospheric conditions. Several solutions have been proposed to solve this problem.
The simplest method for inducing pressure losses between the container and the dispensing tap is to provide a long dispensing line, of a length of about 1 to 5 m. This solution is self evident in most public houses, wherein the kegs are stored in a cellar or next room, connected to the tap by a long line. For smaller systems like home dispensers, however, this solution has drawbacks, such as requiring a specific handling for fitting such long line in a dispensing apparatus, usually coiling it. A substantial amount of liquid remains in the line after each dispensing. Said stagnant liquid is the first to flow out of the tap at the next dispense. This of course has the inconvenience that the beverage stagnant in the dispensing line is not controlled thermally and would result in dispensing e.g., beer at a temperature above the desired serving temperature. A further inconvenient is when changing container, the liquid stagnant in the line may yield serious hygienic concerns and, in case of a different beverage being mounted on the appliance, to undesired flavours mixing. For solving this latter problem, it has been proposed to change the dispensing line each time the container is being changed (cf. e.g., WO2007/019853, dispensing line #32 in FIGS. 35, 37, and 38).
An alternative to increasing the length of the dispensing line for generating pressure losses in a flowing liquid is to vary the cross-sectional area of the line. For instance, it is proposed in WO2007/019852 to provide dispensing lines comprising at least two sections, a first, upstream section having a cross-sectional area smaller than a second, downstream section. Such line can be manufactured by joining two tubes of different diameter, or by deformation of a polymeric tube, preferably by cold rolling. US2009/0108031 discloses a dispensing line comprising at least three sections of different cross-sectional area forming a venturi tube as illustrated in FIGS. 5 and 9 of said application. The dispensing tube described therein is manufactured by injection moulding two half shells each comprising an open channel with matching geometry to form upon joining thereof a closed channel with the desired venturi geometry. In DE102007001215 a linear tube section at the inlet of a pressure reducing duct transitions smoothly into a tubular spiral with progressively increasing diameter, finishing in an outlet opening.
These solutions are interesting but they are not suitable for regulating the flowrate of a liquid when the pressure difference between the container and atmospheric varies over time. Such pressure variations may happen, e.g., in case of pre-pressurized vessels wherein a given amount of pressurized gas is stored in the container. As the liquid is being dispensed, the free volume in the container increases whilst the amount of gas remains constant, thus resulting in a pressure decrease over time in the container. Similarly, when gas is adsorbed on a carrier or stored in a cartridge of small dimensions, the storage capacity may be insufficient to maintain a constant pressure in the vessel over time. A flow rate controlling means able to maintain the dispensing flow rate substantially constant over a given range of pressures in the container is therefore desirable.
In order to solve this problem, a pressure regulating valve is usually used, wherein a flexible diaphragm biased by resilient means, eg. an helicoidal spring, controls the area of an opening; an old and simple embodiment of such valves is given in DE601933 filed in 1933. These solutions, however, comprise multiple components requiring a separate assembly, thus increasing the cost thereof. An alternative to said valves is to control the cross section of a duct by applying pressure to a flexible section thereof.
For example, in order to provide a more accurate control of the flow rate of a fluid flowing in a duct than made possible by the speed control of a pump, it was proposed in EP0037950 to control the cross-sectional variation of a flexible section of said duct by enclosing said section in a chamber connected to a source of pressurizing medium (air, gas, or liquid) able to apply a pressure to said flexible section of the duct. A similar principle is disclosed in CH416245 and in GB2181214. These solutions, however, require a connection to a pressurizing fluid to control the pressure difference across the flexible section of the duct. Furthermore, these systems do not allow the flow rate to be self-regulated but require the control of the pressure of the pressurizing fluid in the chamber to maintain the flow at the desired rate.
FR2426935 discloses a self regulating system for maintaining the level of a liquid in a reservoir fed by a duct within a desired level by immersing said duct at a given distance from the bottom thereof, said duct comprising a section made of two elastomeric diaphragms bond along their lengths and which separation requires the fluid in the duct to be at a pressure higher than the hydrostatic pressure reigning around said section and which magnitude depends on the level of liquid in the reservoir. Although quite ingenious, this solution designed for mud pits or oil drills cannot be applied to beverage dispensing apparatuses.
A self-regulating closure system to be applied in particular to ducts suitable for oil and gas drilling operations is disclosed in U.S. Pat. No. 3,685,538 wherein a section of the duct consists of a flexible sleeve provided on its outer side with a number of pressing rollers which are displaced along the direction of flow in case of overpressure, said displacement comprising a radial component leading to the occlusion of the sleeve. Here again, this system cannot be applied to beverage dispensing means because it is too complex and expensive (even after scaling down) especially for home appliances.
In the other extreme of the size scale of oil drilling ducts, CA2338497 discloses a self-regulating shunt—a small diameter catheter—to be applied subcutaneously in the head of a patient suffering of hydrocephalus to lead cerebrospinal fluid from the head to another space in the body. The shunt disclosed therein comprises a duct having a flexible sleeve section surrounded by a chamber connected to said duct both upstream and downstream with valve systems to compensate pressure variations when a lying patient stands. The flow rate of cerebrospinal fluid is of the order of the ml/s (0.06 l/min) in a purely laminar flow with Reynolds numbers of the order of 1 to 25, not comparable with the conditions encountered with beverage dispensing apparatuses with flowrates of the order of 0.5 to 2.5 l/min and characterized by a mixture of laminar and turbulent flows with Reynolds numbers comprised between 2000 and 4000 or by turbulent flows with Reynold numbers of up to 15,000 depending on the flow rate and diameter of the dispensing duct.
There therefore remains a need for providing flow rate regulating means in a pressure driven beverage dispensing apparatus which is effective in controlling the flow rate over a large variation of pressure differences, which can be produced economically, and which is compatible with the economics of recycling.